Why unmanned cargo carriers are essential to the ISS

Though they don't get as much attention as manned missions, cargo spacecraft are an essential part of advancing space science and exploration - including projects like the International Space Station. CGTN's John Zarrella explains.

You might say the International Space Station is like an orbiting airport terminal with vehicles arriving and departing on a regular basis. The Russian Soyuz spacecraft brings up the crews. But everything the crews need to exist comes up on unmanned cargo carriers.

The Russian Progress ship has done the bulk of the delivery work. Since 2000, the spacecraft has made more than sixty trips to the ISS carrying spare parts, food, clothing, fuel.

But Progress alone could not satisfy the Station’s insatiable appetite.

Until their retirement in 2011, the U.S. Space Shuttles did the heavy lifting. Shuttles were key to building the ISS and bringing up equipment too big to fly any other way. The cavernous cargo bay could hold up to 16,000 kilograms – four to five times more than Progress.

So how do you fill the shuttle void? With a whole host of resupply ships like the Russian Progress, the Japanese HTV, Space X Dragon, and the Orbital ATK Cygnus.

Sierra Nevada’s Dream Chaser should enter the mix in 2019. Dream Chaser would join the Space X Dragon as the only re-useable cargo carriers. The others burn up in the atmosphere on their way back to Earth. None of these vehicles comes close to the cargo capacity of the shuttle, but it’s a lot less expensive and a lot less risky flying these unmanned vehicles.

Tianzhou-1, China’s first cargo carrying spacecraft, is designed to perform like other supply ships. It will dock directly to China’s space station and refuel the it. The Russian Progress does the same at the ISS.

With a five ton cargo capacity it can carry as much, or more, than any of the vehicles servicing the ISS. The success of Tianzhou-1 is a critical step in the development of China’s space program. Because, it’s impossible to have a permanently occupied space station without a means to keep it up and running.